Successful embryo implantation requires correct development of the pre-implantation embryo, resulting in a hatched blastocyst which is able to implant into receptive endometrium. A considerable body of data has been collected which supports the idea that soluble growth factors, if secreted by the uterine epithelium, act directly on the embryo to control this process (Anderson, E. D., J. Cellular Biochem., 53: 280-287 (1993) and Schultz, G. A. and Hevner, S., Mutat Res., 296: 17-31 (992)).
In addition, developing embryos have been shown to produce a variety of cytokines which may act in an autocrine fashion on the endometrium to influence its receptivity. Examples of growth factors shown to be produced by human embryos include IL-1, IL-6, CSF-1 and TNF-.alpha. (Zolti et al, Fertil. Steril., 56 (1991) 265-272 and Witkin et al, J. Reprod. Immunol., 19 (1991) 85-93). TNF-.alpha. has been shown to be present in culture medium of human embryos up to the morula stage, but not that from the blastocyst (Lachappelle et al, Human Reproduction, 8: 1032-1038 (1993)). Production of cytokines by the embryo may therefore be regulated in a stage-specific manner.
Data on the possible direct effects of cytokines on embryos have come primarily from experiments in mice where many cytokines have been shown to affect the development of preimplantation embryos in vitro. RFN-.gamma. and CSF-1, at physiological concentrations, inhibit the number of embryos developing to the blastocyst stage (Hill et al, J. Immunol. , 139 (1987) 2250-2254). TNF-.alpha. has also been shown to have more subtle effects. Although TNF-.alpha. has no apparent effect on rates of blastocyst formation, it appears to specifically inhibit proliferation of cells contributing to the inner cell mass (ICM), which results in blastocysts with a reduced ICM (Pampfer et al, Endocrinology, 134: 206-212 (1994)).
Other growth factors also have specific effects on ICM cells. For instance, insulin-like growth factors 1 and 2 stimulate ICM proliferation, whereas leukaemia inhibitory factor (LIF) inhibits their differentiation (Harvey et al, Mol. Reprod. Dev., 31 (1992) 195-199).
As mentioned above, IL-6 is one of the growth factors which has been shown to be produced by human embryos. IL-6 is a protein which controls the proliferation and differentiation of many cell types in mammals, and in addition has a role in the control of the immune system. Binding of IL-6 to IL-6R initiates the association of IL-6R with a third component known as gp130, which actually transmits the signal through the cell membrane (Taga et al, PNAS, 89: 10998-11001). gp130 is a transmembrane protein, i.e. it extends through the membrane and projects into the cytoplasm, thus it has distinct domains. In this way, IL-6 "signal" transmission is mediated by means of this protein.
EP-A-0411946 discloses a recombinant gp130 protein, as well as DNA sequences coding for such a protein and methods for its cloning.
Yasukawa et al, Immunology Letters, 31 (1992) 123-130, discloses a soluble, recombinant form of gp130, produced by removing the transmembrane and cytoplasmic regions of the membrane bound form of the protein.
Narazaki et al, Blood., 82, No 4 (1993) 1120-1126, disclosed that soluble forms of gp130 exist and may have potential to inhibit signals normally mediated by transmembrane gp130.